1,4-Benzoquinone and 1,4-hydroquinone based determination of electron and superoxide radical formed in heterogeneous photocatalytic systems

In competition-based experiments, 1,4-benzoquinone (BQ) has been a frequently applied compound for determination of the role of O(2)(center dot- )radicals. In those studies, only the influence of BQ (as a competitive O-2(center dot-) scavenger) on the degradation of a model compound (substrate) was investigated. Our goal was to develop a new, simple method monitoring a characteristic product of the reaction between the superoxide radical ion and BQ during heterogeneous photocatalysis. Interestingly, based on our results, if the concentration of BQ exceeds that of dissolved oxygen, it reacts with photogenerated electrons rather than with O-2(center dot-) radicals. During this process, it is quantitatively reduced to 1,4-hydroquinone (H(2)Q), the degradation of which was found to be dependent of the presence of O-2(center dot-) radicals. The photocatalytic transformation of both compounds (BQ, H(2)Q) was systematically investigated in anoxic and oxic atmosphere. Two new methods requiring only fluorescence measurements have been suggested: one for the determination of electrons with BQ (under anaerobic conditions) and another for the measurement of O-2(center dot-) radicals with H(2)Q.